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201.
Ammonium,nitrate and phytoplankton interactions in a freshwater tidal estuarine zone: potential effects of cultural eutrophication 总被引:2,自引:0,他引:2
Rita B. Domingues Ana B. Barbosa Ulrich Sommer Helena M. Galvão 《Aquatic Sciences - Research Across Boundaries》2011,73(3):331-343
Nitrate and ammonium are the most important nitrogen sources for phytoplankton growth. Differential utilization of inorganic
nitrogenous compounds by phytoplankton has been observed and may have significant impacts on primary productivity at local
scales. We used enrichment experiments with natural phytoplankton populations from the freshwater tidal zone of the Guadiana
estuary, a coastal ecosystem increasingly subjected to anthropogenic influences, to study the effects of nitrate and ammonium
on N-consumption and phytoplankton growth. In addition, we used combined additions of nitrate and ammonium to understand the
inhibitory effect of ammonium over nitrate uptake. Ammonium concentrations in the freshwater tidal reaches of the Guadiana
estuary throughout the sampling period were too low to exert an inhibitory effect on nitrate uptake or a toxic effect on phytoplankton
growth. Nitrate was clearly the main nitrogen source for phytoplankton at the study site. Overall, nitrate seemed to become
limiting at concentrations lower than 20 μM and N-limitation was particularly significant during summer. A trend of decreasing
nitrate uptake with increasing ammonium concentrations and uptake suggested an overall preference for ammonium. However, preference
for ammonium was group-specific, and it was observed mainly in green algae and cyanobacteria. In fact, cyanobacteria relied
only on ammonium as their N-source. On the contrary, diatoms preferred nitrate, and did not respond to ammonium additions.
The increasing eutrophication in the Guadiana estuary and particularly increased inputs of nitrogen as ammonium due to urban
waste effluents may result in a shift in phytoplankton community composition, towards a dominance of cyanobacteria and green
algae. 相似文献
202.
Ulrich Knittel 《Island Arc》2011,20(1):138-146
The discovery of a low‐grade meta‐rhyolite with an age of 83 ± 1 Ma documents a so‐far unknown episode of magmatism in northern Mindoro Island, which is located at the northeastern edge of the Palawan Continental Terrane. This terrane is thought to have rifted from Southeast China in the Oligocene as a result of the opening of the South China Sea. Rhyolite volcanism was widespread in southeastern China in the Cretaceous; hence this discovery provides the first direct link between the geological evolution of the Palawan Continental Terrane and Southeast China in Cretaceous time. In addition, it provides further evidence that the northeastern part of Mindoro is indeed part of the Palawan Continental Terrane and not part of the Philippine Mobile Belt to the east, a previously contentious issue. 相似文献
203.
K.M. Campbell J.A. Davis J. Bargar D. Giammar R. Bernier-Latmani R. Kukkadapu K.H. Williams H. Veramani K.-U. Ulrich J. Stubbs S. Yabusaki L. Figueroa E. Lesher M.J. Wilkins A. Peacock P.E. Long 《Applied Geochemistry》2011
Reductive biostimulation is currently being explored as a possible remediation strategy for U-contaminated groundwater, and is being investigated at a field site in Rifle, CO, USA. The long-term stability of the resulting U(IV) phases is a key component of the overall performance of the remediation approach and depends upon a variety of factors, including rate and mechanism of reduction, mineral associations in the subsurface, and propensity for oxidation. To address these factors, several approaches were used to evaluate the redox sensitivity of U: (1) measurement of the rate of oxidative dissolution of biogenic uraninite (UO2(s)) deployed in groundwater at Rifle, (2) characterization of a zone of natural bioreduction exhibiting relevant reduced mineral phases, and (3) laboratory studies of the oxidative capacity of Fe(III) and reductive capacity of Fe(II) with regard to U(IV) and U(VI), respectively. 相似文献
204.
Stanislav Ulrich Ji?�� Konop��sek Petr Je?��bek Lucie Taj?manov�� 《International Journal of Earth Sciences》2011,100(2-3):415-429
Three structural profiles across the Coastal Terrane, the Boundary Igneous Complex and the Orogen Core have been studied in the Kaoko Belt of northwestern Namibia. The oldest known Si fabric is inherited from an older tectono-metamorphic event. It occurs in the Coastal Terrane only and the extent of its reworking increases from south to north. The S1 foliation reactivates or folds Si fabric in the Coastal Terrane and appears as an early planar fabric in granitoids of the Boundary Igneous Complex and migmatites of the Orogen Core domain. Superimposed subvertical S2 fabric corresponds to axial plane cleavage of upright close to isoclinal folds and the extent of its development also increases from south to north. Active migration of partial melt during S2 development in the Orogen Core dates the onset of this deformation at ~550?Ma. Distribution of F2 fold axes and L2 stretching lineations suggests pure shear?Cdominated deformation associated with development of N?CS trending S2 cleavage preserved in the central profile, followed by sinistral simple shear?Cdominated deformation on newly developed NW?CSE trending pervasive cleavage in the northern part of the area. Such spatial variation in the deformation record is attributed to the irregular shape of the Congo Craton indenter that is reflected by heterogeneous development of the S2 cleavage front in the Coastal Terrane and the Boundary Igneous Complex. Common orientation of L1 and L2 stretching lineations and solid-state reworking on both S1 and S2 planes suggest single event of sinistral transpression since 550?Ma with strain partitioning into domains of oblique thrusting (reactivated S1) and transcurrent sinistral shearing (S2 and S3). Such succession of deformation structures suggests that major subvertical shear zones in the Kaoko Belt do not correspond to early crustal discontinuities, but rather reflect late strain localization during cooling. 相似文献
205.
206.
Overview of eutrophication indicators to assess environmental status within the European Marine Strategy Framework Directive 总被引:1,自引:0,他引:1
207.
208.
We present models of temperature distribution in the crust of a neutron star in the presence of a strong toroidal component
superposed to the poloidal component of the magnetic field. The presence of such a toroidal field hinders heat flow toward
the surface in a large part of the crust. As a result, the neutron star surface presents two warm regions surrounded by extended
cold regions and has a thermal luminosity much lower than in the case the magnetic field is purely poloidal. We apply these
models to calculate the thermal evolution of such neutron stars and show that the lowered photon luminosity naturally extends
their life-time as detectable thermal X-ray sources.
Work partially supported by UNAM-DGAPA grant #IN119306. 相似文献
209.
210.
M. Lazrek F. Baudin L. Bertello P. Boumier J. Charra D. Fierry-Fraillon E. Fossat A. H. Gabriel R. A. García B. Gelly C. Gouiffes G. Grec P. L. Pallé F. Pérez Hernández C. Régulo C. Renaud J.-M. Robillot T. Roca Cortés S. Turck-Chièze R. K. Ulrich 《Solar physics》1997,175(2):227-246
The GOLF experiment on the SOHO mission aims to study the internal structure of the Sun by measuring the spectrum of global
oscillations in the frequency range 10-7 to 10-2 Hz. Here we present the results of the analysis of the first 8 months of data. Special emphasis is put into the frequency
determination of the p modes, as well as the splitting in the multiplets due to rotation. For both, we show that the improvement
in S/N level with respect to the ground-based networks and other experiments is essential in achieving a very low-degree frequency
table with small errors ∼ 2 parts in 10-5). On the other hand, the splitting found seems to favour a solar core which does not rotate slower than its surface. The
line widths do agree with theoretical expectations and other observations. 相似文献